Ultrasonic welding may be used to join plastic parts together by rapidly transmitting ultrasonic energy through a shaped tool known as an ultrasonic horn. The energy is in the form of mechanical vibrations creates friction between the parts to generate sufficient heat to melt and fuse together (i.e., weld) the plastic parts. An ultrasonic welder includes an ultrasonic transducer (i.e., an ultrasonic converter). The transducer is housed within a bottom portion of a housing of the welder. The horn is mounted to the bottom end of the transducer and is located adjacent to the bottom housing portion. The transducer may be a piezoelectric element that mechanically vibrates upon being energized, typically by having an electric current applied. The vibration frequency typically falls within a range of 10-50 kHz. As the transducer vibrates at a given frequency, the horn incrementally moves up and down at the same frequency (for instance, on the order of ±0.0004 inches per cycle).
To sonically weld two parts together, the two parts may be co-located and/or Stacked—typically by placing one part on top of another part in a fixture. The horn may then brought into forced contact with the top part while the bottom part is supported by the stationary surfaces of the holding fixture. As the transducer vibrates upon being supplied with electricity, the horn vibrates by reciprocating vertically such that the horn resonates toward and away from the top part. The horn reciprocation in relation to the parts (i.e., the transfer of vibratory energy from the horn to the parts) creates the heat which fuses the parts together.
An ultrasonic welder typically includes either a motor drive assembly for positioning the horn relative to the parts (i.e., for moving the horn towards the parts to bring the horn into forced contact with the parts and for moving the horn away from the parts such that the horn is not in contact with the parts). A typical motor drive assembly may include a motor having a ball screw rotatable drive shaft connected to the exterior surface of the top face of the transducer housing. The motor is driven when powered to rotate the ball screw drive shaft one way causing the transducer housing and the horn to move away from the motor housing and toward the parts to be welded until the horn contacts the top of the part. After the parts are welded together, the motor is driven in response to another electrical signal to rotate the ball screw drive shaft in the opposite direction causing the transducer housing and the horn to move back toward the motor housing and away from the parts after the welding is completed.
In addition to not using compressed air, advantages associated with a typical ball screw motor drive assembly include precise horn positioning as a result of electronically controlling the motor. Electronic motor control also provides indirect information regarding the positioning of the horn (for example, by monitoring the revolutions of the ball screw drive shaft). A position transducer which directly monitors movement of the horn may be employed to provide information regarding the horn positioning. However, a problem with an ultrasonic welder having a typical motor drive assembly is that drive components of the motor drive assembly are not integral with the transducer housing. For instance, the drive shaft is connected to the exterior surface of the top face of the transducer housing. Consequently, the overall size including the height of the ultrasonic welder is relatively large. Another problem with an ultrasonic welder having a typical motor drive assembly is that the drive components do not linearly guide the horn while positioning the horn. For instance, the drive shaft and guide shafts may be connected to the exterior surface of the top transducer housing face resulting in unintentional linear movement of the horn relative to the top transducer housing end (i.e., “wobbling”) which may occur when the horn is in forced contact with the parts to be welded. One example of an ultrasonic welder is disclosed in U.S. Pat. No. 7,438,210, issued Oct. 21, 2008, the disclosure of which is incorporated herein for all purposes.
One known ultrasonic welder is disclosed by Franz Vokurka in his U.S. Pat. No. 4,323,758, issued Apr. 6, 1982, which relates to a known automatic welding machine they may be equipped with only one welding gun. More particularly, Vokurka discloses an automatic welding machine for an arc welder or resistance welder wherein a beam, by means of a carrier, is movably supported by a column, whereby the carrier, both in the direction of its longitudinal extent (Axis B) as well as in a direction (Axis A) perpendicular thereto and parallel to the longitudinal extent of the column, is displaceably guided on the column so that the beam may be displaceable both is a direction perpendicularly (Axis B) to its longitudinal extent (Axis C), as well as in a direction (Axis A) perpendicular to its longitudinal extent and perpendicular to the longitudinal extension of the carrier (Axis B). Further, the beam may include at least two displaceably guided multi-articulated holders for welding guns or pincher guns, and drives may be provided for displacing the holders on the beams and for swinging the articulations on the holders whereby the drives which are coordinated under the circumstances from time to time to the holders or respectively to the welding guns or the pincher guns for making welding seams (which seams run parallel or symmetrical to each other) and may be selectively coupled with each other mechanically or electronically. Vokurka discloses the use of two arc or resistance welding guns mounted in multi-articulated holders on a beam attached to a carrier of an arc or resistance welder that may weld simultaneously but in limited areas where the welding seam runs parallel or symmetrical to each other.